Allow some tags only on top level to fix --tags filtering

[dvkashapov]

The problem: when running ./runtest --large-memory --tags large-memory the --tags large-memory filter would look for tests with large-memory tag, it found the nested tag in the test context but start_server didn't have large-memory, so the filtering logic had issues. And that's why we did not notice how we introduced this failure:

[err]: CVE-2025-32023: Sparse HLL XZERO overflow triggers crash in tests/unit/hyperloglog.tcl
Expected an error matching '*INVALIDOBJ*' but got '1' (context: type eval line 24 cmd {assert_error {*INVALIDOBJ*} {r pfadd hll_overflow foo}} proc ::test)

Tags large-memory, needs:other-server, compatible-redis, and network now restricted to top-level start_server. Prevents --tags filtering issues when these tags appear in nested contexts. Added validation that errors on nested usage. Refactored tests that fail new validation. Also fixed all lsearch calls to use -exact flag to preventing bugs like "tls" matching "tls:skip".

[zuiderkwast]

Awesome. Please also mention in the top comment the problem test case that didn't run in any of our Daily and CI because how --tags -large-memory skipped it and --tags large-memory missed the nested tag because it was under another tag that got skipped.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.98%. Comparing base (839d0c6) to head (79518bf).
⚠️ Report is 8 commits behind head on unstable.

Additional details and impacted files

@@             Coverage Diff              @@
##           unstable    #3171      +/-   ##
============================================
+ Coverage     74.96%   74.98%   +0.01%     
============================================
  Files           129      129              
  Lines         71318    71320       +2     
============================================
+ Hits          53467    53481      +14     
+ Misses        17851    17839      -12     

see 20 files with indirect coverage changes

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[zuiderkwast]

Very good, this should prevent tests from being always-skipped in the future.

[enjoy-binbin]

Thanks!